Traditionally, large vehicles such as trucks and buses have their front steering wheels mounted on spindles at each end of a rigid beam axle. The spindles have integral steering knuckles and are connected pivotally to the ends of the axle beam by king pins which engage the steering knuckles so that the wheels may be turned to steer the vehicle. It is important to maintain the front wheels on these vehicles in proper alignment in order to minimize tread wear and thereby obtain the maximum tread mileage from the tires on these wheels. It has been observed that some radial tires have a tread life of approximately 200,000 miles when mounted on front wheels which are maintained in proper alignment. It also has been observed that the tread life of the same radial tires may be shortened to as little as 40,000 miles when they are mounted on front wheels which are not maintained in proper alignment.
In setting the alignment of a steering wheel mounted at the end of a rigid beam axle, the camber angle and the toe angle of the wheel and the caster angle of the king pin are adjusted. Adjustments of toe angle and caster angle are relatively simple and may be achieved with the use of conventional equipment. However, the classical method of adjusting the camber angle of such a wheel requires the use of special equipment and is relatively complicated. The camber angle of a wheel may be defined as the angle the top of the wheel is offset from a line perpendicular to the ground which extends upwardly through the bottom of the wheel when the wheel is viewed from the front of the vehicle. It also may be defined as the angle the axis of the spindle which mounts the wheel is offset from a line parallel to the ground when the wheel is viewed from the front of the vehicle. In order to change the camber angle the top of the wheel must be moved inwardly towards the body of the vehicle or outwardly away from the body of the vehicle.
In a vehicle in which the steering wheels are not mounted on spindles attached to a rigid beam axle by king pins, the camber angle may be adjusted by inserting a shim between a spindle and a steering knuckle as described in U.S. Pat. No. 4,037,680 and U.S. Pat. No. 4,195,862. The vehicle described in these patents has a driving front axle, a steering knuckle mounted in ball joints at each end of the axle, and a spindle bolted to the steering knuckle. Using a shim to set the camber angle of a wheel has a number of disadvantages. One disadvantage is that it is difficult to position a shim between a spindle and a steering knuckle such that bolt holes in the shim are aligned with bolt holes in the spindle and in the steering knuckle so that bolts can be inserted in the holes to attach the spindle to the steering knuckle. Another disadvantage is that it is necessary to mantain an inventory of different sized shims to obtain different camber angle settings. A device for changing the angle of a spindle rigidly mounted on a nonsteering axle which utilizes a pair of tapered rings having toothed ends may be seen in U.S. Pat. No. 774,042.
In large vehicles having rigid beam axles, the spindles and steering knuckles traditionally are one-piece units which are mounted pivotally on the ends of the axle by king pins. Consequently, there are no assemblies between which shims may be inserted to adjust the camber angle in these units. One mechanism for adjusting the camber angle for a spindle and steering knuckle mounted on an axle by a king pin utilizes a sleeve having an eccentric king pin bore as described in U.S. Pat. No. 3,342,507. However, this mechanism requires a substantial number of parts and is complex. The classical method of moving the top of the wheel inwardly or outwardly to adjust the camber angle of a steering wheel on a rigid axle of a large vehicle entails bending the axle. The axle may be bent at its center to simultaneously move the tops of both wheels outwardly (to make the camber angles of both wheels more positive) or inwardly (to make the camber angles of both wheels more negative) or it may be bent at one or both ends to change the camber angle of one wheel or to change the camber angle of both wheels in opposite directions.
It is undesirable to bend rigid beam axles in order to change the camber angle of the front steering wheels for a number of reasons including the fact that the axle may break while it is being bent. Additionally, the seats for the front leaf springs in the vehicle are distorted when the axle is bent which may cause premature wear of the spring leaves which contact the seats. Also, when the spring seats are distorted, the springs are twisted and spring pins which pass through bushings mounted in the ends of the springs to anchor the springs, contact the outer ends of the bushings instead of the inner surfaces of the bushings and cause the bushings to wear prematurely. Furthermore, in some instances, an axle manufacturer will void the warranty of an axle which is bent to adjust the camber angles of wheels mounted thereon. In this situation the axle has to be replaced which is extremely expensive. In addition, special tools and equipment are required in order to bend an axle.
It is desirable to provide a spindle adapted to be pivotally mounted by a king pin on the non-powered, rigid beam axle of a vehicle which will support a steering wheel and which will permit the camber angle of the wheel to be adjusted facilely and inexpensively without bending the axle and without requiring the use of additional parts of special tools.